In recent years, a great deal of study has been conducted to improve dye-forming couplers for silver halide photosensitive materials. While many significant advances have been reported, the best couplers available today still have serious deficiencies. In particular, improving the stability of the image dyes derived from cyan couplers has proven to be very difficult.
The couplers commonly used to form cyan image dyes in color films and papers are generally of three types: amides of 1-hydroxy-2-naphthoic acid as represented by formula (I) and described in U.S. Pat. Nos. 2,313,138; 4,208,210; 5,283,163; 5,380,638; 5,476,757; and 5,457,020; 2,5-diacylaminophenols as described by formula (II) and described in U.S. Pat. Nos. 2,369,929; 2,895,826; 3,466,622; 3,758,308; 3,864,366; 3,880,661; 3,996,253; and 4,333,999; and 2-acylaminophenols as described by formula (III) and described in U.S. Pat. Nos. 2,367,531; 2,369,929; 2,423,730; 2,801,171; 3,772,002; 3,998,642; and 4,560,630. These types of couplers can be used either by being incorporated in the photographic silver halide emulsion layers or externally in the processing baths. In the former case the couplers must have ballast substituents built into the molecule to prevent the couplers from migrating from one layer to another. ##STR1##
In each of the formulas (I), (II) and (III), R.sub.1 represents an alkyl, aryl or arylamino substituent and Z represents a hydrogen atom or a group which is split off during the coupling, reaction ("coupling-off group"). In (II), R.sub.2 represents an alkyl or aryl substituent, usually an alkyl group substituted at the alpha position by an aryloxy group. In (III), R.sub.3 represents an alkyl group, usually methyl or ethyl, and X represents a halogen atom, usually chlorine or fluorine.
Although the couplers of formulas (I) and (II) have been used extensively in color photographic film products, the dyes derived from each of the three types suffer from various deficiencies that make them unsatisfactory for use in color photographic papers. The couplers of Formula (III) are commonly used in color photographic papers, but they nevertheless have serious shortcomings that will impose limitations on their use in future paper products that will have much more stringent requirements.
Couplers of Formula (I) yield image dyes that have poor stability to heat, humidity, light, and ferrous ions that are present in the bleaching solution. Furthermore, the absorption spectra of their image dyes are too bathochromically shifted (that is, shifted too far toward the long wavelength portion of the spectrum) to be useful in color photographic paper, and the dyes have an unacceptable side absorption in the short wavelength portion of the spectrum.
The image dyes derived from couplers of the 2,5-diacylaminophenol Formula (II) have excellent stability to heat and humidity, but they have poor stability to light. Furthermore, while the short-wavelength side absorption of these dyes is sharper-cutting than in the case of formulas (I) and (II) the hues of the dyes are too hypsochromically shifted (that is, shifted too far toward the short wavelength portion of the spectrum) if R.sub.1 is alkyl or aryl, and too bathochromically shifted (toward longer wavelengths) if R.sub.1 is arylamino, to be useful in color photographic paper.
The couplers of the 2-acylaminophenol Formula (III), more specifically those of Formula (IV), are used in nearly all commercially available color photographic papers. The couplers of this type that have been commercially used may be divided into two groups according to the substituent group R.sub.3. When R.sub.3 is a methyl group, the image dyes have excellent light stability but suffer from insufficient stability to heat and humidity to meet the requirements of modern products; on the other hand, when R.sub.3 is an ethyl group, the stability to heat and humidity is greatly improved but light stability is unsatisfactory. Even when R.sub.3 is an ethyl group, the stability to heat and humidity is not good enough to satisfy the stringent requirements of future color papers. ##STR2##
Examples of these couplers are shown in U.S. Pat. No. 4,828,970 and in EP 554,027 but none of the R.sub.4 /R.sub.5 substituent combinations disclosed provides satisfactory results.
A problem to be solved is to provide a color photographic element containing a silver halide emulsion layer having associated therewith a cyan dye forming coupler that forms a more stable dye than heretofore obtainable.